Design and testing of the Lunar Thermal Mapper optics

The Lunar Thermal Mapper (LTM) is a compact multi-band push-broom infrared radiometer on the NASA Lunar Trailblazer mission due to launch in 2024. The LTM optics consists of a fast (F1.5) 5-mirror diamond turned free-form system. The mirrors are machined from lightweighted aluminium blanks with integral mounting flexures. The system is assembled on an athermal aluminium optical bench to maintain alignment through the launch and under the challenging thermal environment of lunar orbit. With this novel optical system LTM achieves high resolution infrared imagery in a compact, low mass instrument. We present the design and model performance of the optics, details of the optomechanical design and manufacture, and results from AIT of an optical breadboard and LTM flight model instrument. As the LTM optical system is seeing reuse for future missions (such as MIRMIS on ESAs Comet Interceptor) we discuss the use of the LTM optical design with higher resolution detectors.